Installing a 240 Volt Inverter

An inverter is really an essential item in your RV, as it converts 12 volts DC from your battery or solar cell into household style 240 volts alternating current. This makes your RV even more like "home". If you know nothing about inverters then this article is for you, as even if you have no intention of installing one yourself, it will make you more conversant with what you need to buy or have fitted! As usual this is another minefield area, and yes it is so easy to make expensive or inadequate size or type mistakes. Generators and inverters both perform the same task. The difference is that an inverter only uses power when the connected device requires it. A generator chugs away even under no load and is noisy and a polluter and you cannot always use it - National Parks etc.!

Please remember safety when messing with inverters.

Electricity from an inverter can kill you just as quickly as the normal mains, particularly if you don't bolt it into your RV. Some inverters can be quite lethal if used in the boot of a car for instance and a fault develops. At the outset please note that we will be CONTINUALLY stressing safety throughout this article. At one stage we abandoned this story because of all the safety problems we encountered, but then realised if we did nothing no one will find out about the dangers and pitfalls. The photo below is the TBS 150 watt unit.
 

Pictured below: Left is the SEA 150 watt Piccolo (not double isolated) - centre the 200 watt Selectronic - right is the 500 watt Tempo made by SEA. This unit has a double pole switch, overload and works "on demand". The RRP is $1199.00.

Modified Sine Wave Inverters

There are basically two main types of inverters on the market. The cheaper MODIFIED SINE WAVE more or less imitates 240 volts by "chopping" bits out - sometimes called "simulated sine wave". This is a bit like driving on a pot holed road - not at all smooth. This is fine for many crude applications where so called "dirty" electricity works OK (power tools) but is totally unsuitable for things like laptop computers, printers and scanners. Some of the really low cost entry models are not too good on TV either, as you get lines on the screen even though ads can say they are OK. The only way to find out is to take your electrical bits and pieces to your supplier and try them on the inverter you are interested in. Modified sine wave models start from under $100.00 with the "plug into a cigarette lighter models". Yes folks, as usual we have bought one of these with absolutely disastrous results, so we are totally qualified to say don't do it, as they are a total waste of money!

Pure Sine Wave Inverters

The other type is FULL SINE WAVE - also called "pure". These start at around $300.00 for 100 watts. In our view you are better off going for a top quality full sine wave inverter right from the outset, otherwise you will find yourself "upgrading" only a little bit further down the track. Full Sine Wave produces 240 volt AC that is usually cleaner and more reliable than that in your own home and it will be free from spikes and other nasties that can kill delicate electronic equipment. Interestingly the output voltage is to a much closer tolerance than the mains - usually within 2%. So using a sine wave inverter ensures that all your equipment operates exactly the same as they would when powered from your AC wall outlet at home! A powerful argument for buying the best! The diagram below shows you graphically how the sine wave flows smoothly and the modified or "square wave" is lumpy.
 

Think before you buy!

You do need to do some heavy thinking before racing out and buying your first inverter. It is one area where BIGGEST IS NOT BEST! This is because all inverters consume electricity even when idle - about 10%. This is proportional to size. In our view trying to run a microwave in your RV is totally daft and will only lead to dissatisfaction and disappointment with your system. You can find out the horrific technical reasons for this by reading Motorhome Electrics and Caravans Too! by long time motorhomer Collyn Rivers. Our best advice is to go with the SMALLEST sinewave unit that will meet MOST of your needs, rather than go for the much larger wattage's offered by the modified units. If you use computers you have an easy choice! A good move is to find a fellow A'vanner with an inverter and try your gadgets with it. Just because the appliance has a LOWER WATTAGE than the inverter you intend buying doesn't necessarily mean it will work with your appliance. We had a 50 watt TV and a 100 watt nasty inverter and yes it wouldn't work as the INRUSH current needed to fire up the tele couldn't be delivered. A separate video on the other hand worked OK. All good sinewave inverters are designed to produce up to twice their continuous rating, for a few seconds, and about 130-150% for 10-30 minutes. These are not damaging overloads - they are intended to work this way.

What we do with ours

Rather than give you heaps of calculations with formulas, here it is in a format you can easily understand with no technical mumbo jumbo at all. We worked out what we needed to run and set ourselves a realistic limit of 150 watts. Ouch I hear you say - I can't do anything with that! Well you can in fact do quite a lot. Below is a list of all the electrical items we run - not altogether though mind you! All of these items can easily be run using a single A'van battery without flattening. (100 AH is minimum - 120 AH would be better)

	Stab mixer for soups
	Tooth brush charger
	Sony digital camera charger
	Orion TV video combination (also runs on 12 volt)
	10" oscillating fan
	Sony Vaio laptop computer (also used for watching DVD)
	Toshiba laptop computer
	Charger for Psion Revo - email
	Iomega zip drive - X 2 - USB
	Yamaha Spyder CD burner - USB
	Acer 15" LCD computer monitor
	Orange juicer
	Sewing machine - Husqvarna

Maximum loadings

Bear in mind that many items draw far more current than what's on the label. Our 30 watt fan actually uses over 100 watts as it uses an inefficient induction motor! For a better understanding of this we suggest you have a read of What's Watt by successful author Collyn Rivers. Our maximum load which we run for around 4 hours a day in bright sunshine is both laptops and the zip drive. In high summer we run one computer and the fan. We only use one computer when running the LCD monitor (40 watts)  - used for watching DVD and editing photos. We use all this gear sensibly and use our brains on dull days. A good excuse to veg out! If you are ordering a new A'van and feel you will need to run gear similar to what we are doing it would be a good move to fit a 60 watt or larger solar panel. It is easy to get the upgrade during manufacture, but much harder later on. Remember that you can run the panel across the roof and not just the normal way that A'van do it - between the front bubbles.

Circuit diagram

The circuit diagram below shows you just how simple this project is. Make CERTAIN that you put an inline or blade type fuse or DC overload breaker very close to the battery in the POSITIVE cable. We also installed a 15 amp self resetting overload to be doubly sure as these are under $10.00! We put this very near the battery as well. If you don't have terminal crimping pliers your only alternative is to use an inline fuse and electrical connectors. The TBS also has its own built in safety features. It turns off with under/over voltage as well as overload and short circuit. Be very careful not to reverse polarity. We did not test what happens but Collyn Rivers assures us it would wreck the inverter! Dearer inverters such as the Selectronic LD range are reverse polarity proof. Wire colours shown below are for illustration purposes only. It is very important to ask your supplier if the inverter case should be earthed or not. In the case of TBS the advice we received from Holland was to keep the case ABOVE EARTH (in English this simply means do not connect to the metal frame of the vehicle - explained in detail below).

Overloads and Safety

Another point you should be aware of is that many low end inverters are no longer electrically safe when hard wired into your A'van and in many the RCD WILL NOT TRIP under fault conditions. This article is not concerned with this type of installation at all but our research indicates that the Selectronic and SEA units (both made in Australia) are very good choices for this application. Expect to pay around $1200.00 for a 500 watt unit with automatic standby. The installation MUST be done by a qualified electrician. Don't forget to ask for a small pilot light if you cant see the front panel of the inverter.

For these reasons we prefer to keep our system separate from the A'van 240 volt system, BUT we do not neglect safety at all. There are a few options available with the TBS. Mount it so that the ready to plug into outlet is easily accessible. The TBS comes with an IEC320 computer style socket. You find these sockets on computer monitor leads that plug into the computer case. A plug is supplied with the TBS. You can either get your electrician to fit it to a short lead or a small power board if you cant find a lead ready made. You could be better off avoiding these hassles by buying an inverter with a standard 3 pin plug such as the Piccolo. The photo below shows a TBS mounted in a 2B. It was made for this A'van and fits beautifully. DO NOT CONNECT TO ANYTHING METAL. In our 3C we surface mounted it just above the Arlec charger. This worked well but looked ugly. The photo shows a simple surround made using plastic trim available from Bunnings etc.

NOTE:- Be aware that many inverters (the TBS in this case) will not trip an RCD if you buy a special safety lead with one built in. We are not too happy about this at all despite assurances from TBS, so we ONLY use double insulated appliances with this particular inverter. We make it a Golden Rule not to use appliances outside the A'van.
 

The TBS has an on demand function they call "automatic standby mode" (ASB). It stays in standby mode until a load is detected - drawing just 10 watts. Works great, but we don't use it, as it is actually still using valuable battery power when waiting for load. It also has a self diagnostic mode. Different flashing light combinations indicate specific faults.

Installation

Select a location where the DC low voltage cable run will be the shortest possible distance, as the longer a DC cable run is the greater the voltage loss. Select a cable at least the same diameter as the fly leads coming out of the unit. In our case we used the cable already fitted to the unit - about a metre long. This also eliminated the need for joins. If you MUST have longer leads you could use 6mm automotive cable by Tyan. It would not be overkill to use light 8 mm starter motor cable. Ventilation is an important factor to consider. The TBS unit does have an inbuilt fan, but as with even the best inverters you already lose up to 10% just to run it, so you don't want the fan cutting in all the time. We normally surface mount, but in this case the little lady insisted on a "prettier" installation, so it went under the bed!

TBS inverters

This is actually our second TBS inverter and we have had zero problems. However we now have more knowledge and all future inverters we buy will be double insulated (isolated). Ours cost $400.00 from Battery World at Slacks Creek in Brisbane - zero web presence. We received excellent technical advice (but we didn't ask the right questions!) with zero high pressure. We found the Australian importers Bainbridge Technologies in Brisbane - very hard to deal with either by phone or email. TBS is a Dutch company and have an excellent, very informative, all in English website - www.tbs-electronics.nl/inverters/ps150.html. Requests for info via email is always same day! Pretty impressive and very, very friendly. We actually cannot praise them enough we just wish they would upgrade their insulation. We have included some of their answers to technical queries below as it shows that they are aware of the problems and will be bringing out improved models in 2003. For heavy inverter users not owning a Plasmatronic monitor unit, they have a similar unit that tells you current usage and an estimate of what is left in the battery if you keep using power at the present rate. Handy gadget and really looks the business - lots of info on their website with top pictures. We DON'T profess to be inverter experts, and if you own Collyn Rivers book he will more than likely answer questions for you on this topic as he certainly has an excellent grounding in this field. The 150 watt has a surge rating of 350 watts and the weight is 2.1 KGs.

The next size up is 225 watts and this costs around $525.00. (non isolated at present) Remember though that having more watts requires more battery and solar, and batteries are heavy gadgets. Models above 150 watts have a rocker switch next to the outlet.

Optional Power (02) 9450 0709 have the Piccolo - RRP $494.00 and $445.00 to CMCA members. It has a standard 3 pin 10 amp socket on the front and is a bright canary yellow - it is NOT double isolated. Dave Lambert of the Rainbow Power Company (sales@rpc.com.au) has the Selectronic, but the best prices seem to be the 12 Volt Shop but freight from WA could gobble up the savings. We have found them extremly slow to answer questions via email (10 days!), however at the Barcaldine Rally they were very helpful on their trade stand. All Selectronic units are double isolated.

Jaycar Inverters

Collyn Rivers suggested we contact Jaycar and we certainly did hit gold for those on a tight budget. Just go to www.jaycar.com.au and enter the catalogue number into the search engine. Jaycar have two inverters - we couldn't get the first one to come up when we tried.

150W sine wave inverter cat# MI5080 $AU299 electrically Isolated 300 W sine wave inverter cat# MI5082 $AU379 electrically Isolated

Designed as a free-standing inverter, this 300-watt model boasts electrical isolation between battery and secondary (mains) voltage for increased safety. The build construction is outstanding, too. The inverter is housed inside a tough aluminium case with heavy-duty heatsink and includes a cooling fan for added reliability. DC connection to the inverter is made via heavy duty binding terminals, ready to accept between 14 and 6 gauge hi-current cable. Other features include low profile mains socket, on/off switch, low battery alarm and shutoff, plus a tri-state LED indicating over temperature and overload conditions, etc. Most importantly, the overload characteristics of this inverter are excellent. This means that it will be more successful in starting up colour TVs and hand tools, for example. Easily one of the best non-industrial and cost effective inverters we have ever seen. Specifications: Output Power: 300W continuous Surge Power: 500W. Standby Current: <0.6A Input Voltage: 10.7V - 15VDC Output Wave Form: Sine Wave Efficiency: 85% Typ. Output Regulation: +/-3% Output frequency: 50Hz Cooling: Internal Fan Low battery Alarm: 10.7V Low batt shut Off: 10V Overload: Shutdown Battery Reverse: Internal Fuse Input Connectors: 6 gauge Dimensions: 107(W) x 60(H) x 280(L)mm Weight: 1.65Kg. One Year Warranty. Both these units are the cheapest wattage sine wave units currently available and Jaycar is a solid reliable supplier, however we haven't come across any motorhomer using one as yet. Country of origin is not mentioned but the specs read

Summing Up

We cannot emphasise too much that you are working around 240 volts. Please observe the law for your own safety and have a licensed electrician finish of this project for you. Remember that most low end inverters are not safe when hard wired into your A'van's 240 volt system.

Bob Eustace

Acknowledgements - Special thanks to Collyn Rivers - Geoff Adcock (CMCA), and TBS (Holland)

Safety Notes - It is important that you read this!

Whilst it is legally OK to install an inverter with a 240 volt socket attached to the inverter case into the 12 volt supply, we cannot stress how important it is for fellow A'vanners not to attempt to install an inverter into the fixed 240 volt wiring. DO NOT buy an inverter that doesn't have a three pin socket built directly into the housing unless you are having it installed by a licensed electrician who is familiar with RVs. There is a very valid reason for this in that inverters in Australia (at present) do not need electricity authority approval unless they are hard wired into a 240 volt system. In our view this is a really poor show on the part of the authorities, but it certainly explains the huge price differences between the el-cheapo high wattage units and top line products such as the Australian made Selectronic and SEA . When buying an inverter we strongly suggest you ask the supplier the following:

• Is the inverter double insulated (electrically isolated between the battery and secondary voltage)?
• Can the inverter DC and AC circuits be earthed?
• Will the inverter work properly with an RCD?

If the answer is NO to ANY question please don't buy! Being double insulated means that should a fault develop, there is just about zero chance of 240 volt feeding back into the 12 volt system. As things stand at present there are a lot of units out there which run the risk of failing in this quite catastrophic way. Rvs with everything metal "live" at 240 volts aren't an attractive proposition at all and it can be lethal. Some very responsible retailers have withdrawn a few models with this problem in the past few months. We were first made aware of this problem when a fellow club member pointed out some anomalies when using some brand inverters with safety switches (failing to trip). It is amazing what one can discover when pointed in the right direction. In using our TBS unit we make sure that the case is above earth (not in contact with metal) and its supply battery and case is not connected to the motorhome frame as it is not isolated. Our next RV will probably have a small Selectronic LD350-12 or an SEA Tempo unit. This is a far more expensive option ($1200.00) but you can't put a price on safety. We will certainly consider TBS if their units are then isolated. If you don't need pure sine wave Jaycar Electronics have several low cost units all isolated models. The general feeling amongst sparkies is that inverter rules are likely to be tightened in 2003. Our personal view for what its worth is, we would like to see the sale of ALL non-isolated inverters totally banned in Australia as many motorhomers are possibly blissfully unaware of the problems if they are not mounted above earth. One very pleasing thing that did emerge doing this article is the manufacturers really do care and will bend over backwards to answer questions often of a "hairy" nature.

Below is the info we received from TBS in response to a query we raised on concerns about double insulation/isolation. Yes we did misread their manual and there are in fact warnings in their instructions. Sorry TBS! Please don't hesitate to write to Daniel if you need more technical information on their inverters.

Hello Bob,

It is not as alarming as you've stated. Surely, non isolated DC-AC inverters have some limitations in a few applications. Since the 150W units are our low budget models, we have had to consider the method of output voltage feedback based on cost price. All this of course within the specific safety regulations required for inverters. Non isolated feedback is four times cheaper than isolated feedback. Our models AL450i-12 and up, are equipped with isolated outputs. However this inverter will most likely be overkill for your application. Our current AL225i-12 and AL275i-24 inverters are being redesigned at this moment. One of the changes which will be made is isolated feedback. These redesigned units will be available 1st quarter of 2003. We have no plans to alter the 150W units.

With regard to the AL150i-12 construction. On page 2 of the manual, the following caution statement is printed :

"The inverter's case is directly connected to the outlet earth terminal. The DC input wires are not directly connected to the inverter's case, only for high frequencies. Inverter input and output are not galvanically isolated."

The AL150i-12 is not more dangerous than an isolated unit being mounted on a chassis. In both cases, failing isolation could lead to an enclosure carrying a lethal voltage. The AL150i-12 enclosure is completely floating from the internal electronics (only coupled for high frequencies), so there is no direct potential electrically attached to the unit's enclosure. The only difference between an isolated unit and a non isolated unit is that DC side ground is direct connected to the AC side ground. It is technically NOT possible that , in case of malfunctioning, 240V could appear on the DC side. In this very rare case the sinewave generator and bridge control will directly shutdown leaving nothing to be fed back to the input. The fact that no safety standard nor our local safety agency KEMA mentions a non isolated inverter to be dangerous, underlines the above statement.

So, what are the drawbacks of non isolated inverters and why are we implementing isolated feedback in our new redesigned 225W and 275W units? When an installation contains an inverter powered by a battery which in turn is connected to an appliance (i.e. a battery charger) that has some electrical connection with the inverter's output too, a ground loop is created which could cause some stability problems in the inverter's output voltage. In some cases customers in the martime sector, would like to attach a phase or neutral from the inverter's output to it's enclosure. This way a new earth circuit can be created. This method is not possible with a non isolated unit and could damage internal electronics. For these reasons we are implementing isolated feedback in all our new units.

If you have any further questions, please do not hesitate to ask.

Best Regards,

Daniel Schouten - Product Design & Management
TBS ELECTRONICS

daniels@tbs-electronics.nl

Using ELCBs with inverters

We received the following information from Michael Rush of Selectronic in Bayswater, Victoria. Safety is very important when dealing with 240 volt so it is a good idea to take onboard Michael's comments. You can contact him at mrush@selectronic.com.au.

Use of ELCB protection devices on Selectronic inverters in portable situations

Introduction
The purpose of this report is to consider the use of Earth Leakage Circuit breaker (ELCB) protection devices with an inverter when used in a portable situation. We will investigate the type of ELCB which may be used, their usefulness and limitations.

Background
A Selectronic inverter takes power from a DC source, normally a battery, and converts it to AC power (normally 240V) suitable for running standard mains operated appliances. The output is just as hazardous as mains power therefore the same precautions should be taken when operating appliances from an inverter as you would from a normal mains outlet.

It is important that you read and understand the user manual that came with the inverter and follow the safety recommendations when using the inverter. If you have any questions after reading the user manual, please contact Selectronic and we will always be happy to assist.

When using the inverter, never operate any faulty appliances, and if in doubt have the appliance checked by a qualified person. Also never operate any appliance in a hazardous situation and always follow the appliance manufacturer’s recommendations when operating any appliance from an inverter.

Using ELCBs in a portable situation
A portable situation is defined as connecting the inverter to the battery supply and using the inverter via the front power point. In this situation it is assumed the inverter is not connected to an earth stake, and that the output has not been connected MEN (earth and neutral connected together). When used in this configuration, the output is ‘floating’ above earth and any ELCB connected between the inverter and the appliance will not trip in the event of a fault within the appliance. This is because there is no return path for the ‘fault’ current and therefore the ELCB does not detect any imbalance in the load current. Likewise if there are more than one faulty appliance connected to the inverter via an ELCB, then the ELCB would still not trip. This is because any fault currents would flow between the appliances via their earth connection after the ELCB. Therefore the ELCB would again see a balanced current as no fault current would bypass the ELCB.

In a portable situation, the ELCB would only trip in the event of a fault between the live terminals and case within the inverter together with a fault between the live terminals and case within the appliance (assuming the appliance is earthed and not double insulated). These faults would need to be such to cause sufficient fault current to flow though the earth connection between the inverter and the appliance before the ELCB would trip.

When an ELCB is required to be used with an inverter in a portable situation, only an external plugin type or external inline type should be connected to the inverter. Under no circumstances should the GPO (power point) on the front of the inverter be removed or replaced with an ELCB type GPO.

Conclusion
The use of an ELCB with an inverter in a portable situation does offer the user a greater level of protection than not using one, however it should be noted that the ELCB will normally not trip in the event of an appliance fault. It is therefore important to ensure the appliances and the inverter are regularly checked for safety.

Michael Rush - mrush@selectronic.com.au

UPDATE 14th September 2002

We have an Arlec Inverter which we bought at Dick Smith's for around $162. It plugs into the cigarette lighter in the A'van and has power points to connect 240 watt appliances up to 300 watts. So far we have found it to work very well.

Elaine Cronin - Queensland